Process printing is used with different kinds of printing operations. In general, the process color set has a limited number of colors, such as black, cyan, magenta, and yellow. Full color prints are made by color separating the original image into tone values of the process colors. The color separations can be printed sequentially and/or overlapped to produce the full-color print of the original image.
Unfortunately, a four-color ink set often cannot reproduce the full gamut of colors of the original image. One approach has been to use one or more spot colors, i.e., custom inks of a particular color, to print colors not achievable with the four-color ink set in an additional printing step. While this can produce truer colors, the spot colors complicate the printing, increasing cost. The spot colors must be selected to match the desired color, custom ink prepared, and printing steps added to print the additional colors. In addition, the printing equipment must be thoroughly cleaned so the spot colors do not contaminate future print jobs. The custom ink is only usable for the particular job, so left-over ink is often wasted. Some attempt may be made to reblend the left-over ink into another formula, but the reblended formula is no longer pure and may be susceptible to metamerism.
Another approach has been to increase the number of ink colors in the process color set. Unfortunately, even a color ink set with an increased number of ink colors often cannot produce the range of colors desired: the number of inks may not be adequate or may not be the right mix of colors to produce the desired colors. Often, the range of hue of a reduced gamut will not be able to produce the final color desired.
Another problem with process printing is obtaining colors from the production run which match the selected sample colors. Typically, sample colors are printed with an ink jet printer or other printing device and colors are then selected from the sample colors. The inks and production presses are set up to match the selected sample colors for the production run. Unfortunately, the colors in the final image may not match the selected sample colors: the sample colors may not match the actual results due to differences of printing on the production presses, as well as differences of the printing characteristics of the underlying substrates. Samples can be printed with the production presses and the ink and printing process adjusted to tune the production colors to the selected sample colors, but this increases the time and expense of printing and often requires pre-press approval by the customer.
It would be desirable to have an eleven-color printing ink set and method of use that would overcome the above disadvantages.